I also have a tissue valve and got back into weights (after a 20 year break) about 1 year and 2 months post op. Never had any issues including when I did a 1 rep max. I did make sure I was breathing properly as I heard that to be the biggest risk (holding your breath while pushing up). Good luck.
I'd also suggest that you start light and see how it feels. I don't bench, but I do a lot of push-ups. It took almost a full year before I felt comfortable doing sets of 50+ without sternum or muscle pain. Of course, YMMV, as I was 63 at time of surgery.
I re-started doing bench press as part of my weight lifting routine at 3 months post op when my cardiologist said "no restrictions". I started with low weights and ever so gently adding on. I'm now 11 months post up and lifting 19 kgs (42 pounds) bench press - doing super slow technique so making sure I breathe freely and fast throughout. Have tissue valve - age 60 at time of surgery. Looking forward to getting back to what I did before surgery !
When I had my Ross Procedure on July 30, 2012 I'm pretty sure I was back in the gym lifting weights around late October 2012. As long as you don't feel pain, you should be fine. Start light and continue to work up to what you used to be. I was 24 when I had my surgery and had a pretty quick recovery as I'm sure you are now.
Another word of caution (not heart related)...I have learned that when you are getting back into it, there is no such thing as going too easy. Each time I get back into it, I think I am going light enough and am then sore for the next week.
Since learning about my BAV I took to heart not lifting weights (or anything that required me to hold my breath). Since my ross procedure in july of this year I plan on continuing to never really do any weight training as I feel its not worth it (granted I'm more into cardio). That is just a personal view. I do agree with TOM IN MO to breath while doing any exercise....I did that yesterday bringing in the 45 lb cat litter from the car.